Submitted by Mrs. Applebee from Junction City, KS on July 22, 2004
Sea turtle researcher Catherine McClellan, who is based in Beaufort, North Carolina, shares her knowledge of sea turtle research methods.
Questions and Answers
Question #1.
What is the purpose of tracking sea turtles?
Answer:
Sea turtles spend the majority of their lives underwater and far away at sea. The ocean is a rather hostile environment for humans, therefore we know very little about the turtles. By tracking them remotely (like with satellite transmitters) we can learn where they go, where they spend their time, and what types of environments they occupy.
Humans have been developing many technologies to allow them to venture farther and farther into the ocean and have found many used for its natural resources. However, they have put little effort into considering what impact they might be having on the ocean. Fishing, for instance, frequently results in unintentional catch of certain species (known as by-catch) like turtles. Different fishing gear types have different impacts. Some are also harmful to the habitat. By tracking the turtles and combining their locations with other information (like fishing or environment) we can see what threats they might be facing.
The goal of this project is to look at sea turtle interactions with fisheries in North Carolina. By understanding how turtles use habitat and looking at where fishing occurs, we hope to identify hot spots for problems and advise the fishing community on where potential problem areas or potential safe areas within a season might be.
Question #2.
What are some different tracking methods used to track sea turtles?
Answer:
Because sea turtles spend most of their time under the water it is very difficult to follow them visually (such as by following them in a boat), so there have been several techniques that were developed to do this remotely. One is called acoustic telemetry. This is a device that you can put on the animal which emits a sound that you can hear underwater with a special device called a hydrophone. Usually acoustic tags can be heard within a one kilometer (0.6 miles) range. The accuracy of these devices is usually quite good, but you have to be relatively close to an animal to find it. So this would work near shore, or you'd have to be in a boat to follow the animal around. This is very labor intensive (a lot of work), so studies are usually relatively short in duration unless the animal does not move far and would be easy to find again after you went home.
Another method for tracking sea turtles is with radio telemetry. This device can also be put on a turtle, but cannot be heard in salt water. So the device has an antenna that sticks up in the air when the turtle surfaces to breathe. The antenna sends out a signal into the air and if you are listening with your own electronic equipment (an antenna and a receiver) you can hear the signal. Radio tags can be heard within a eight kilometer (5 miles) range (or more if you have more powerful equipment-boosters). You hold your antenna in the air and listen for the signal and then determine the direction it is coming from and where the signal is the strongest. There can be quite a bit of error in this method, so you usually try to move to different places and listen again or have multiple people with antennae and receivers stationed in various spots all listening at once. This process is called triangulation because you draw lines to the direction of the signal from each listening point and form a triangle (or polygon) to determine the approximate location of the animal. Again, you need to be relatively close to the animal and you need to be quick in determining the location direction and hope the turtle doesn't submerge again before you determine the location. This is also requires a lot of work from one person or multiple persons because you are actively searching for the animal.
Satellite telemetry also sends out radio signals (much stronger) from a transmitter through an antenna into the air when the turtle surfaces to breathe. But this time a series of polar-orbiting satellites are continually listening for the signals. When the satellite hears a signal, it determines the location of the animal using the Doppler-shift (see http://science.howstuffworks.com/radar1.htm for more information). The satellite then sends the animal's location to the scientist through email, in the mail or on a CD. This is great because you can sit in your comfy office and wait for the data to come to you. Studies can be long in duration (limited only by the battery power of the satellite transmitter), and the animal can be virtually anywhere in the world and you still get a signal.
However, the accuracy of the location varies with the time the animal spends on the surface and other interference in the air. A satellite also has to be passing overhead when the animal surfaces to hear the transmission. Sometimes the estimated location can be very wrong. Therefore there are tradeoffs to using each method and it really depends on the question you are asking for which method would be best for you. There are other types of tags, such as PIT (passive integrated transponders) tags or flipper tags, but these are only a physical tag and do not transmit a location. You need to find the animal again so you only know where the animal was and where it is now, but not where it has been in between.
Question #3.
What do researchers learn from tracking sea turtles?
Answer:
There are many questions researchers ask when tracking sea turtles:
- Some just want to know where they go and when they go there.
- Some want to know how they use habitat and what kinds of habitats they prefer (sea grass, coral reefs, open ocean, muddy bottoms, ocean currents, etc.).
- Others want to know what kind of things influence their movements (water temperature, prey, wind, earths magnetic field).
- Some want to know what threats they might be facing (fishing, shipping traffic, harvest).
- Many are interested in nesting patterns and locations and how frequently they come back to nest.
- Some transmitters also record data like depth and temperature so you can find out how deep they dove and where in the water column they spend most of their time, or what are the thermal preferences and tolerances of the animal.
- Some just want to compare what one animal did with another animal given the same conditions—say a rehabilitated animal compared to a healthy wild caught animal.
I think the more we learn from tracking sea turtles, the more questions that arise!
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